Interplanetary Magnetic Field Control of Polar Ionospheric Equivalent Current System Modes

Abstract

We analyze the response of different ionospheric equivalent current modes to variations in the interplanetary magnetic field (IMF) components By and Bz. Each mode comprises a fixed spatial pattern whose amplitude varies in time, identified by a month‐by‐month empirical orthogonal function separation of surface measured magnetic field variance. Here we focus on four sets of modes that have been previously identified as DPY, DP2, NBZ, and DP1. We derive the cross‐correlation function of each mode set with either IMF By or Bz for lags ranging from −10 to +600 mins with respect to the IMF state at the bow shock nose. For all four sets of modes, the average correlation can be reproduced by a sum of up to three linear responses to the IMF component, each centered on a different lag. These are interpreted as the statistical ionospheric responses to magnetopause merging (15‐ to 20‐min lag) and magnetotail reconnection (60‐min lag) and to IMF persistence. Of the mode sets, NBZ and DPY are the most predictable from a given IMF component, with DP1 (the substorm component) the least predictable. The proportion of mode variability explained by the IMF increases for the longer lags, thought to indicate conductivity feedbacks from substorms. In summary, we confirm the postulated physical basis of these modes and quantify their multiple reconfiguration timescales.

Spatial Variation in the Responses of the Surface External and Induced Magnetic Field to the Solar Wind

“…Two of these four major spatiotemporal patterns of variability in the SEIMF (viz., DP2 and DPY) are predictable from the solar wind perturbations. This subjective interpretation was justified further by Shore et al ().…”

Data‐Driven Basis Functions for SuperDARN Ionospheric Plasma Flow Characterization and Prediction

“…(2010) found higher correlations between the IMF and nightside geomagnetic variations, compared to dayside variations. The cause of this correlation difference was identified by Shore, Freeman, and Gjerloev (2019). The authors proposed that because sustained IMF B z driving will likely lead to a substorm event, then on average we expect increased particle precipitation and conductivity in the auroral zone at longer lags.…”

“…In other words, we find that both the plasma drift (i.e., the electric field) and the magnetic field respond to direct driving with the same latency, when ionospheric conductance is high enough to produce a detectable magnetic perturbation. The long lag time taken for VPY and IMF B y to become decorrelated is due to the long autocorrelation of IMF B y with increasing lag (see Shore, Freeman, & Gjerloev, 2019).…”

“…This allows us to offer a technique to provide an infill solution without resort to external information (e.g., the solar wind). If desired, the dependence on the solar wind or substorms can later be determined separately for each mode (Shore, Freeman, & Gjerloev, 2019). This allows us to provide a semi‐automated characterization of the electrodynamics in a manner similar to the historic component approach, but based on many more data.…”

Geomagnetic Responses Associated With Throat Aurora

“…It has been long known that any external magnetic perturbation comprises ionospheric equivalent current system which is driven mostly by interplanetary magnetic field (IMF) (e.g., Nishida, 1966Nishida, , 1968Obayashi & Nishida, 1968). This results in two cell ionospheric current vortices driven by and Bz (Friis-Christensen & Wilhjelm, 1975;Friis-Christensen et al, 1985;Hairston et al, 2005;Maezawa, 1976;Nishida, 1968;Shore et al, 2019). The By (dawn-dusk component) is basically responsible for the DPY current pattern (Friis-Christensen & Wilhjelm, 1975;Friis-Christensen et al, 1985).…”